For measuring trees, there is no difference in accuracy. Think of it this way - 1 arc-sec = the width of a dime viewed from 1.25 MILES away. So even with 10 arc-sec, you're looking at something the width of 10 dimes, about 5 inches, from 1.25 MILES. So across an acre, you'd be down do the 1/2 dime range or less. And, as usual, your setups and instrument leveling will degrade your readings more than anything.
Oh, and don't forget to use an offset measurement to get the center of tree measurement.